1. Field of the Invention
This invention relates to avian egg micro-crack detection systems and to methods for using the systems.
2. Description of the Related Art
The contents of an avian egg are enclosed with two shell membranes and a shell. An eggshell check is defined as an opening in the eggshell with the shell membranes intact and no egg contents voided. A crack is an opening in an eggshell where the membranes are compromised and egg contents are voiding through the opening. To detect checks and/or cracks in shell eggs during processing, the egg industry uses high-speed acoustic systems. Once the eggs are processed and the desired percentage of checked or crack eggs are removed, the remaining eggs are boxed for sale. Prior to shipment, human graders sample a grading lot of eggs (currently 100) to ensure that the high-speed systems are operating within specifications for a given grade of egg, such as, Grade A Large Eggs. Currently these human graders use a longstanding technique of visually candling and audibly “belling” an egg to detect defects such as checks or cracks. Belling an egg is a technique that includes gently tapping two eggs together and listening for a dull sound. The dull sound is an indication of a check or crack. Once heard, the grader then visually confirms there is a disruption in the shell. In some of the high-speed sorting and grading systems, very small egg cracks, known as micro-cracks, can occur and initially go undetected by the human graders. Although a large number of automatic inspection devices have been proposed, candling of eggs in a direct light source is still used by human inspectors to validate the grade of a lot. When the number of eggs processed in a graded facility is large, there is a need to increase the number of inspectors. Moreover, there is an upper limit to the accuracy and speed at which the inspectors can operate because of the concentration required. Fatigue is a major limiting factor.
Various automated systems have been used to detect checks and cracks and include tapping of eggs so that a check or crack can be recognized from the type of sound which develops from the tapping, (see for example, Canadian Patent No. 927,965 issued Jun. 5, 1973 to Bliss). Alternatively the change in elastic characteristics can be noted by tapping with a small hammer, which recoils less from places, which are cracked, (see for example Dutch Patent Application No. 286,485). If an egg is vibrated, a damping of the vibration on the cracked places can be detected.
Examples of previous patents or patent applications which have attempted to solve the problems are as follows:
East German Application No. 293,340, published Aug. 29, 1991 discloses utilizing the intensity of light transmitted through eggs as a criterion to distinguish between flawed and perfect eggs.
European Patent Application No. 373,261, published Jun. 20, 1990, discloses locating the eggs on a conveyor roller track at high speed while examining them by a detector. Flawed eggs are discharged from the conveyor at an appropriate position downstream of the inspection station.
Dutch Patent Application No. 8,303,804, published Jun. 3, 1985 provides a system for alleviating operator eyestrain.
U.S. Pat. No. 4,487,321, issued Dec. 11, 1984 to Bliss, utilizes an elongated pointer for movement into and out of engagement with eggs. Signal generators respond to pointer movement for generating signals for identifying the position of selected articles when they are engaged by the pointer.
U.S. Pat. No. 4,182,571 issued Jan. 8, 1980 to Furuta et al., utilizes light reflection signals obtained from light beams passed through an egg to select eggs containing blood.
U.S. Pat. No. 4,161,366 to Bol et al. and issued Jul. 17, 1979, utilizes a laser as a light source to scan the egg. The intensity of light penetrating into the egg is measured. Part of the light penetrating into the egg is diffusely reflected and part is absorbed while entering the shell, particularly in the case of brown eggshells. The light that penetrates inside the egg is strongly scattered by the shell structures. This scattered light is dissipated by multiple reflections of the inner surface of the shell and the yoke sac. The egg glows uniformly. The light radiating from the egg corresponds to the structure of the shell. In particular, the egg shines more brightly when the scanning light beam falls on thin, glassy spots of the shell or cracks. In some instances, an actual flash of light may even be observed.
The process and system of the invention of U.S. Pat. No. 4,161,366 generates a characteristic flash of light for cracks, pinholes and regions of thin shell caused by cage marks or body checks. Some of these flaws may be acceptable but a flaw characterized by an actual disruption of the shell integrity never is acceptable. It is therefore, important to distinguish between checks and cracks and other shell-related flaws.
U.S. Pat. No. 5,615,777 (Apr. 1, 1997) discloses an egg candling system which scans the surface of an egg for flaws such as pin holes, cracks, thinned shell regions, etc. using a laser beam. The light beam is vibrated with a rocking/rotating movement to describe a closed curve such as a circle, ellipse, or an ellipse so narrow that it is effectively a straight line. The utilization of such a light beam allows identification of flaws due to the character of the progression of light emanating from the egg. The patent further discloses an apparatus for rotating the egg about its longitudinal axis in the path of the beam or beams. The apparatus also includes apparatus for forming the vibrating beam such as mirrors vibrated by out of phase electro-magnetic vibration or piezo-electric actuators.
Lin et al. (ASAE Paper No. 99-6071, Jul. 18-22, 1999, Toronto, Ontario, Canada) disclose a non-destructive method for measuring eggshell strength using loading and unloading of hydrostatic pressure on eggs. One aspect of the disclosure was to determine the loading pressure needed to extend cracks on the eggshell. They found that when the hydrostatic pressure was suddenly removed from the tested egg, the micro-crack would extend. Their preliminary results showed that a smaller pressure drop from loading to unloading could make egg checks and cracks more visible.
De Ketelaere et al., (World's Poultry Science Journal, Volume 60, 289-302. September 2004) reports the use of impactor technology for eggshell crack detection. One device uses a small impactor to excite the eggshell. The amplitudes of the rebounds are measured to determine eggshell integrity. The reference then reports another impactor method where an egg is rolled over a series of small metal objects under which a piezo-sensor is mounted. It is alleged that this measuring principle reveals only local shell quality information and the crack detectors have to test several locations for each egg in order to obtain satisfactory results. In another approach, the response of the egg itself to the impactor is considered by looking at the number of resonant peaks.
While various systems have been developed for detecting checks and cracks in eggshells, there still remains a need in the art for a more effective system for detecting cracks and checks, especially micro-cracks to assist graders in validating the grade of an egg. The present invention, different from prior art systems, provides a system which uses negative pressure and an imaging system to enhance crack detection.